Custom JSON (Un)Marshaler in Go

main.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/url"
	"strings"
)

type Scope []string

func (s *Scope) MarshalJSON() ([]byte, error) {
	if s == nil {
		return nil, fmt.Errorf("scope is nil")
	}
	return []byte(fmt.Sprintf("%q", url.QueryEscape(strings.Join(*s, " ")))), nil
}

func (s *Scope) UnmarshalJSON(d []byte) error {
	elems := make([]string, 0, 5)
	err := json.Unmarshal(d, &elems)
	if err != nil {
		return err
	}

	*s = elems

	return nil
}

func (s Scope) String() string {
	return url.QueryEscape(strings.Join(s, " "))
}

type MyConf struct {
	// just some data, like an actual config
	Host  string
	Scope Scope
}

func main() {
	cfg := MyConf{
		Host:  "localhost:8080",
		Scope: []string{"api", "email", "profile"},
	}
	data, err := json.MarshalIndent(cfg, "", "\t")
	handleErr(err)

	fmt.Printf("%s\n", data)

	cfg2 := MyConf{}
	err = json.Unmarshal(data, &cfg2)
	handleErr(err)

	fmt.Printf("\n%+v\n", cfg2)
}

func handleErr(err error) {
	if err != nil {
		log.Fatal(err)
	}
}